Thank you @Chad and @andrewatfornax for discussing this. On the topic of generating a CI for each email, could you use the recipient's email address? Many ESPs will provide merge codes for that so that even if you're using the same email template to send to 500 people, the emails can have a different CI for each recipient. For example, SendGrid has a [%email%] merge code and MailChimp has a *|UNIQID|* merge code. The former is the plain email address while the latter is, I believe, a hashed version of the email address. That would at least eliminate the need for a Revive user to generate GUIDs per email.